GA4 will be the new standard on July 1st, 2023, and standard Universal Analytics (UA) accounts will cease collecting data at that time. Thankfully, setting up a new GA4 property is quite simple. You can see the walk through on this page from Google:
Long story short, you can login to your existing UA property, click admin in the lower left, make sure your correct UA account is selected from the dropdown in the Property column. Click the GA4 Setup Assistant option and step through the steps. That property should use your existing Google Analytics code on your site, so you don't actually need to change any of the coding on your site at all.
Once you do the initial setup, there are some additional setup steps you can do to take full advantage of the GA4 functionality that is described a little more on this page:
You can setup some of that additional functionality by going to that same Admin --> Property Column section and click the "Setup Assistant" link which will help you walk through more of that.
This GA4 property should start collecting data for you as soon as about 30 minutes after the initial setup. It should also collect that data right alongside your existing Universal Analytics account. Then on July 1st, your Universal Analytics account will no longer collect data, and you'll need to rely on just your GA4 property.